1. Field of the Invention
This invention pertains generally to phase shifters associated with array antennas and more specifically to a device utilizing stripline/slotline transitions to facilitate digital shift of the electromagnetic signal phase in an antenna array.
2. Description of the Related Art
Microstrip patch antennas for flat phased antenna arrays, date back to the 1950's and have been reviewed by D. M. Pozar. See, D. M. Pozar, Microstrip Antennas, Proc. IEEE, Vol. 80, No.1, pp. 79-91, Jan. 1992. Their development has been driven by systems requirements for antennas with low-profile, low weight, low cost, easy integrability into arrays with polarization diversity or with microwave integrated circuits. This antenna is basically comprised of a feed layer, selected intermediate layers, and a radiating antenna having one side exposed to free space, in some cases through a radome layer. In order to scan the antenna beam, each antenna element must be equipped with a phase shifter; however, low-cost, small-size phase shifters are unavailable at the present time.
Circuits forming the intermediate layers of a patch antenna are comprised of a dielectric substrate covered by patterned metallic, electrically-conductive sheets used to convey electromagnetic power among electronic components such as phase shifters. One form of circuit is a transmission line known as microstrip, a planar structure consisting of two sheets of electrically conductive material, the two sheets being spaced apart by a single dielectric substrate. One of the sheets is etched to provide strip conductors which in cooperation with the other sheet (ground plane) supports a transverse electromagnetic (TEM) wave. Two other forms of planar transmission lines known as stripline and slotline are used in this invention.
This invention utilizes a type of phase shifting circuit board that combines stripline with slot line to form a small, efficient, low-cost phase shifter that may be incorporated with an aperture coupled patch antenna. See, D. M. Pozar, Flat Lens Antenna Concept Using Aperture Coupled Microstrip Patches, Elect. Ltrs., Vol. 32, No. 23, pp. 2109-2111, Nov. 1996.